1. Field of the Invention
This invention relates to a disk array apparatus having a plurality of disk drives for storing data, controlling these disk drives and writing and reading out the data to and from a high order apparatus, and a data relay method of this disk array apparatus.
2. Description of the Related Art
Generally, a disk array apparatus having a plurality of disk drives for storing data, controlling these disk drives and writing and reading out the data to and from a CPU (Central Processing Unit) for an information processing unit (high order apparatus) comprising a computer having memories has been proposed.
This disk array apparatus includes a disk control apparatus and disk drive apparatuses. The disk control apparatus is arranged at the center and the disk drive apparatuses are arrange on both right and left sides. The disk control apparatus controls the overall disk array apparatus. Each of the disk drive apparatuses accommodates disk drives. Various devices such as hard disk drives and semiconductor memory devices can be used for the disk drives.
The disk control apparatus includes a management terminal, a control circuit unit, a cooling fan, a power source unit, and so forth. The management terminal is arranged on the front surface. An operator can perform maintenance and management of the disk array apparatus by using this management terminal.
The control circuit unit is the unit to which various devices for governing control of the overall disk array apparatus are mounted. The devices mounted include a channel adaptor (channel control unit), a disk adaptor (disk control unit), a cache memory, a shared memory, etc, that will be later described. The cooling fan is used for cooling the disk control apparatus. The power source unit supplies power that is necessary for operating the disk arrays.
A large number of disk drives are arranged in the disk drive apparatus. The disk drives are detachably accommodated inside a disk drive casing of the disk drive apparatus. The disk drives are accommodated not only on the front surface side of the disk array apparatus, that is, on the same side as the management terminal, but also on the rear surface side.
A patent reference 1 listed below discloses a disk array apparatus. The disk array apparatus has a plurality of hard disk drives (HDD) and controls data write/read to and from these hard disk drives by utilizing a Fibre Channel Arbitrated Loop (hereinafter called also “FC-AL loop”) and a Port Bypass Circuit (hereinafter called also “PBC circuit”).
FIGS. 18A and 18B show the arrangement of a plurality of disk drives 4 and a PBC board 20 having mounted thereto the PBC circuit 14 of a conventional disk array apparatus inside a disk drive casing 3a. Four PBC boards 20 are arranged at the center inside the disk drive casing 3a perpendicularly to the arrangement direction of the disk drives 4 and sixteen disk drives (hard disk drives) 4 each having a two-stage construction are arranged in the horizontal direction (row direction) on the right and left sides of these four PBC boards 20.
PBC circuits 14 formed by two LSI and constituting two systems are mounted to each of the four PBC boards 20 as shown in FIG. 19, a plurality of relay connector 21 interface-connecting to each of a plurality of disk drives 4 are mounted, and the PBC circuits 14 of the LSI and a plurality of relay connectors 21 are connected and wired with one another.
Connection between the relay connector 21 of the PBC board 20 and the ports of each disk drive 4 is made through a data transfer route using wirings 22a in the row direction and disposed on a rear surface substrate 22 fixed to the rear surface of a plurality of disk drives 4 as shown in FIG. 18B.
Patent Reference 1:
JP-A-2001-222385
Incidentally, communication at transfer rates of 1 Gbps and 2 Gbps has already been put into practical application in the FC-AL (Fibre Channel Arbitrated Loop) loop by employing a loop structure by serial transfer, and development of communication at 4 Gbps has now been under way.
The biggest problem for this high-speed serial transfer is the printed substrates such as the PBC boards 20 and the rear surface substrate 22. In such printed substrates, a dielectric loss becomes greater at a higher frequency in addition to a conductor loss and a skin effect and eventually a high frequency component attenuates which is equivalent to the case where the signal is passed through a low-pass filter.
Since the rise of a pulse subjected to band limitation gets dull, attenuation of short wavelength components and inter-symbol interference (ISI) develop and deteriorate signal quality of the Fibre Channel signals. A line width of an eye pattern on the reception side of the disk drives 4 and the PBC circuit 14 gets thick, noise and jitter become more vigorous and a bit error ratio (BER) drops due to the drop of the aperture ratio of the eye pattern.
As a result, the transfer loss becomes great in proportion to the wiring length and to the transfer frequency of the Fibre Channel signal transfer path on the printed substrate. In other words, attenuation of the Fibre Channel signal (FC signal) and the inter-symbol interference (ISI) become great in proportion to the wiring length L between the PBC circuit 14 and the disk drive 4 on the rear surface substrate 22 and quality of the Fibre Channel signal drops.
To cope with the drop of quality of the Fibre Channel signals described above in the conventional disk array apparatus, the PBC boards 20 having mounted thereto the PBC circuit 14 for connecting transmission/reception ports of a plurality of disk drives 4 in a loop form and transmitting and receiving the Fibre Channel signals are arranged at the center positions with respect to each of the disk drives 4 of mounting groups (sixteen groups, for example) arranged in the horizontal direction as shown in FIG. 18A. Therefore, the wiring lengths L in the horizontal direction between the disk drives 4 and the PBC circuits 14 on the rear surface substrate 22 are different depending on the mounting positions.
For instance, in the case of the disk drive 4a nearest to the PBC substrate 20, wiring can be made at the shortest wiring length of about 25.4 mm that is the width of the disk drive 4a as the wiring length L on the rear surface substrate 22. In the case of the disk drive 4b that is most spaced apart from this PBC board 20, on the other hand, the wiring length L on the rear surface substrate 22 is about 203.2 mm that is eight times the width of this disk drive 4, i.e. 25.4 mm. The wiring length L on the rear surface substrate 22 becomes greater in accordance with the number of disk drives 4 mounted.
In the conventional disk array apparatus, therefore, quality of the Fibre Channel signal varies in accordance with the mounting positions of the disk drives 4 on the back end. As the wiring length L on the rear surface substrate 22 becomes greater, attenuation of the high range components resulting from the transmission path loss, the drop of quality of the Fibre Channel signals resulting from the inter-symbol interference (ISI), and so forth, become greater.
In view of the problems described above, this invention aims at improving the drop of quality of the Fibre Channel signals in accordance with the mounting positions of the disk drives.